In a conventionally known device that radiates light onto a living body and detects light emitted from the living body to evaluate a health condition, for example, of the living body, use of an optical photo detector (OPD) using an organic semiconductor has been studied in recent years.
The OPD can be formed on a flexible substrate, and thus is very useful for measurement of a living body having a curved surface. For example, Patent Document 1 describes a pulse sensor in which a light source and an organic light-receiving element are provided on a flexible substrate.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2008-103670